There is new evidence supporting a controversial theory that humans began changing the earth's climate with the development of agriculture some 8,000 years ago.
In an article published in the journal Nature, researchers studying the theory say new data indicate that enormous amounts of earth-warming greenhouse gases released into the atmosphere by early farming activities helped ward off an impending ice age, and fostered the planet’s current relatively warm, stable climate.
A more commonly accepted theory suggests that man’s first major influence on the earth’s climate began in the 18th century, at the dawn of the industrial age.
Scientists say the new findings indicate that the earth was spared from another long deep freeze after the last Ice Age ended 11,000 years ago because of an unusual rise in atmospheric carbon dioxide and methane gas levels starting about 3,000 years later.
The increase coincided with the advent of farming practices - including the clearing and burning of forests, and maintaining large herds of livestock - that released more of those heat-trapping gases into the atmosphere.
Prehistoric climate expert William Ruddiman of the University of Virginia first proposed the theory in 2003. He said the new findings supporting his hypothesis will be published in a series of papers later this year in a special issue of the journal The Holocene.
Critics of the theory say human populations 8,000 years ago were too small to produce enough greenhouse gases to influence global climate change. And they suggest that other causes, including changes in the earth's orbit and a variety of natural events, could explain the unusual rise in greenhouse gases.
Greenhouse gases are man-made and naturally-occurring gases that trap solar heat in the earth’s atmosphere.
Most scientists now believe that modern man’s burning of fossil fuels and the clearing of forests over the past two centuries have intensified the so-called "Greenhouse Effect" and have caused a gradual warming of the earth's climate.